The present invention relates to etching of a substrate in a plasma of process gas.
Electronic devices, such as integrated circuits, are formed by deposition, growth (such as by oxidation, nitridation, etc.) and etching of material on a substrate. In a typical etching process, a patterned etch-resistant mask is formed on the substrate by a conventional photolithographic process, and thereafter, exposed portions of the substrate are etched away with energized gases. In the etching process, a reactive gas is introduced into a chamber and is supplied with electromagnetic energy, such as microwave or radio frequency energy, to form an energized gas, such as a plasma, to etch the substrate. In addition, a biasing voltage may be applied to the plasma to energize charged plasma species to provide more anisotropic etching.
In the etching process, it is desirable to control the dimensions of the features being etched, and it also desirable to etch features, such as openings or trenches, with smooth vertical sidewalls. However, conventional etching processes often result in non-uniform etching rates and microloading effects across the substrate. Microloading is a general term used to describe undesirable variations in etch rates, feature shapes, or other etching attributes, from one etched feature to another and across the substrate. For example, the etching rates of the etched holes may vary between small diameter holes which have a high aspect ratio and large diameter holes or open spaces. As another example, the shape or etching rates of the etched features may vary from regions of the substrate having a high density of features (dense feature regions) to regions having relatively few and isolated features (isolated feature regions). Critical dimension microloading may also arise from the variations in critical dimensions of the etched features, the critical dimensions (CD) being those dimensions that are used to calculate the electrical properties of the etched features in the design of integrated circuits. For example, the cross-sectional area of an interconnect line or contact is a critical dimension that should be close to predetermined dimensions to provide the desired electrical resistance.
Accordingly, it is desirable to etch features, such as holes and interconnect lines, across the substrate at uniform and reproducible etch rates. It is further desirable to reduce variations in the etching rate of the high aspect ratio holes relative to open spaces on the substrate. It is also desirable to obtain etched features having uniform and predictable shapes.